Thermostatic switch



Aprii 22, 15341. F. c. EVANS THERMOSTATIC SWITCH Filed Nov. 27, 1937 2SheetsSheet l INVENTOR F. C. EVANS BY i 8 ATTORNEY April 22, 1941. F. c.EVANS THERMOSTATIC SWITCH Filed Nov. 27, 1937 2 Sheets-Sheet 2 FIG. 5.

FIG. 4

INVENTOR F. C. EVANS U23 ATTORNEY Patented Apr. 22, 1941 THERMOSTATIC'swrron Francis C. Evans, Dongan Hills, Staten Island, N. Y., assignor toAmerican District Telegraph Company, New York, N. Y., a corporation ofNew Jersey Application November 27, 1937, Serial No. 176,784

9 Claims.

to direct radiation from the area in which fire may occur, while on theother hand the possibility 'of sending in false alarms by pressingagainst the exposed parts or otherwise tampering with the thermostatshould be prevented. In addition the thermo-sensitive element and anyother movable exposed element of the thermostat should be so mounted andshielded that it will not be afiected by a deposit of dirt, dust, or oreven of other foreign material, such as paint, on the exposed membersduring long periods of use. Furthermore the contacts of a thermostaticswitch, where the alarm or temperature-responsive device includes aswitch, should be adequately sealed to minimize deterioration of thecontact surfaces by dirt, moisture or fumes since the switch may beinstalled for long periods of time before the occurrence of a fire andupon such occurrence must operate infallibly.

It is an object of the present invention to provide a thermostaticdevice fulfilling these requirements.

Another object of the present invention is to provide a thermostaticswitch embodying an improved sealed contact construction.

Another object of the invention is to provide a thermostatic switch ofthe type that employs a bi-metallic cupped disc thermostat member foroperating the switch contact and arranged so that the connection betweenthe disc member and the switch does not bias the thermostat to affectthe adjustment of the same or the temperature at which it operates.

Another object of the invention is to provide a thermostatic device ofthe type wherein the thermo-sensltive member is exposed in whichimproved means is provided for shielding the thermostat element andassociated parts so that the operation will not be affected by a depositof dirt or other foreign material.

A still further object of the invention is to provide an electric switchhaving the contacts thereof sealed in a simple and effective manner.

Other objects and advantages of the invention will appear from thefollowing description of the preferred embodiment thereof shown in theaccompanying drawings wherein:

Fig. 1 is a bottom or plan view of a thermostatic switch particularlyadapted for use as a ceiling thermostat for a fire alarm system.

Fig. 2 is a side elevational view of the thermostatic switch shown inFig. l in which apart of the base is shown in'section in order toillustrate the internal construction more clearly;

Fig. 3 is a top plan view of the switch shown in Figs. 1 and 2;

Fig. 4 is a cross section taken on the line 3-4 of Fig. 2; and

Fig. 5 is a fragmentary view on an enlarged scale of the movable contactand operating member with the thermostatic disc shown in the op eratedposition.

Referring to the drawings, the thermostatic switch illustrated comprisesa substantially circular base member to which may be molded of Bakeliteor other suitable insulating material. The base member ID is providedwith a peripheral recess II to receive the terminal plates or contactsl2 and a central recess i3 forming a contact chamber. The diameter ofthe body portion of the base member Hi is preferably so chosen that theswitch may be mounted on the cover of an outlet box and project througha knockout hole of the box. The upper or rear portion of the base memberI0 is provided with two apertured lugs I5 to facilitate the mounting ofthe switch either in an outlet box or by means of screws to the ceilingof the space protected by the alarm system. Obviously the shape andconstruction of the switch base may be widely varied in accordance withthe requirements of any particular installation. without departing fromthe scope of the invention. As shown, the lugs l5 project beyond thebody portion of the base so that a cover may be fitted to the rear ofthe base between said lugs to enclose the circuit terminals. The basemember ID is further provided with peripheral portions 16 of reducedcross section adjacent the terminal plates l2 whereby openings for thecircuit wires or conductors may be provided by breaking out theseportions, as indicated in the lower part of Fig. 3.

The switch further comprises two stationary contact members 20 adaptedto be bridged by a movable contact member 2i which is mounted on the endof a movable operating member or stud 22. The contact members 20 may bemolded in the base member i0 and be either integral with or extend intocontact with the terminal plates [2 whereby the conductors or wiressecured to said plates are connected together when the operating stud 22moves the bridging contact member 2| into engagement with the stationarycontact members 2d. The switch may also be arranged to break instead ofmake an alarm circuit when the operating stud 22 moves from its normalto its operated position by reversing the position of the contactmembers with respect to the movable contact member 2i.

The movable operating stud 22 for actuating the switch contact 2|projects through an aperture 23 in the base member W, the cross-sectionof the aperture 23 being larger than that of the stud 22 to obviatefrictional engagement between the stud and the base. The stud 22' isalso provided with an enlarged shank portion 25 adjacent the head 26,the inner end of said shank portion being formed with a narrow or sharpsealing ring 21 adapted to effect a tight seal for the contact chamberby engagement with a sealing gasket or washer 28 (see Fig. 5). Theoperating stud 22 is normally urged in an upward direction by a helicalspring 29 to maintain the sealing ring 21 against the gasket or washer2d, the length of the stud being sufiicient to prevent contact betweenthe head 26 thereof'and the thermostat disc 30, as clearly shown inFigs. 2 and 4, when the stud is in its normal or upper position.

In the embodiment shown, the thermosensitive element 30 comprises abi-metallic cupped thermostatic disc member having a central aperture toreceive the operating stud 22, and supported at its edges by a pluralityof grooved supporting members 3| projecting from the base member Ill.The disc member 30 is thus mounted in spaced relation to the opposingsurface of the base member ID with the low expansion convex surface ofthe disc adjacent said base member whereby the thermostatic member isexposed to free circulation of the ambient medium and the highexpansionmetal on the underside of said member is directly exposed toradiant heat. It will be evident that maximum sensitivity and rapidityof operation is insured by this relationship. -The bimetallic cuppeddisc member 30 per se is well known and requires no detaileddescription. The disc member snaps from the position shown in Figs. 2and 4 to that shown in Fig. 5 when the member is heated above theoperating temperature. The mounting of the disc member as shown has thefurther advantage that the switch can not be operated by pressing on theexposed outer surface so that accidental or malicious false operation ofthe alarm is practicallyimpossible.

Since the head 26 of the stud 22 is disengaged from the disc member 30until the disc member snaps to the alternate position shown in Fig. 5,the adjustment or operating temperature of the thermostatic element isnot affected as would be the case if the center of the disc member wererestrained in its initial movement. Furthermore the disc member, inoperating, strikes the head of the stud 22 a hammer blow which breaksloose any deposit of dirt or paint which may have accumulated on .theexposed parts. As' shown, the sealing gasket 28 is preferably disposedin a recess in the base member It! to prevent the formation of a heavydeposit of dirt or other foreign matter at this point.

The contact chamber may be sealed at the rear by a cover 34 and a layer35 of suitable sealing composition. Thus a hermetic seal is obtainedwithout imposing a frictional load on the operating stud 22, which sealis effective until the sealing ring 21 breaks contact with the gas- 7ket 28, and the contact surfaces of the contact members 20 and 2! do notoxidize or tarnish even after the device has been installed for a longperiod.

In order to further protect the exposed thermostatic disc member 30against the formation of dirt or paint deposits at the points of supportof the edge of said disc member sufficient to affect the adjustment andsensitivity of the device, means such as a guard ring 36 is provided toenvelop or shield the edge of said disc member, at least where the sameengages the supporting members 2!, The guard ring is also carried by themembers 2| as shown or may be supported in any convenient manner. Thusif the thermostatic switch is subjected to a paint spray or installed ina dust-laden atmosphere, the guard ring 36 collects the foreign matterwhich would otherwise impinge upon the edge of the disc member 30without substantially shielding the thermo-responsive element fromconvection currents or radiant heat. The guard ring also serves theadditional purpose of protecting the thermostatic disc from accidentalinjury, such as that which might be caused by a person inadvertentlyhitting or brushing against a mounted thermostat with a ladder or otherbody. The ring also guards the thermostat against injury which might becaused by a careless installer dropping the thermostat from the ceilingwhile making an installation. The base member ID is also provided with adepending lip 3'! outside the periphery of the thermostatic disc member30 to prevent dripping of moisture on the member 30 where condensationoccurs on the underside of the base of the switch.

It will be apparent from the foregoing description of the preferredembodiment of the invention that I have devised a novel thermostaticdevice which may be exposed for long periods of time to relativelyadverse conditions of use and which after such exposure will operateinfallibly. As described, the connection between the thermostatic discand the operating stud will insure the proper functioning of the deviceat a definite predetermined temperature. The positioning of theelectrical contacts in a sealed chamber protects these contacts fromcorrosion or other deterioration which would occur if they were leftexposed to ordinary atmospheric conditions.

The device provided by the present invention is susceptible to a numberof modifications, which will be obvious to one skilled in the art,within the scope of the appended claims.

I claim:

1. A thermostatic electric switch comprising a base, cooperating contactmembers in a recess in said base, means for sealing said recess,thermostatic means outside of said recess and a frictionless actuatingconnection from the thermostatic means to said contact members wherebythe thermostatic means is unbiased by friction during operation.

2. A thermostatic electric switch comprising a base having a recess andan aperture, a movable contact member in said recess, thermostatic meansincluding, an operating member for said contact member projectingthrough the aperture in said base and having a lateral sealing contactsurface engaging the base, the cross-section of said operating memberbeing smaller than that of said aperture whereby said means is unbiasedby friction during operation.

3. A thermostatic electric switch comprising a base having a recess, amovable contact member base having a recess, a movable contact member insaid recess, an operating member for said contact member extendingthrough the base, a bitherefor cooperating with said disc member butnormally disengaged therefrom for providing impact movement thereof by.said disc, said supporting members and said operating means therebyproviding for the unbiased operation of, said disc member.

7. A thermostatic electric switch comprising a base having a sealedchamber, cooperating contact members disposed in said chamber, operatingmeans for said contact members, said means extending outside of saidchamber, an annular sealing surface formed on said operating means,

metallic thermostatic disc member mounted on said base and adapted toengage said operating member, a sealing washer surrounding saidoperating member, and resilient means for holding said operating memberin sealing engagement with said washer.-

5. A thermostatic electric switch comprising a base having a recess, amovable contact member in said recess, an operating member for the'contact member extending through the base, a bimetallic thermostaticdisc member mounted on said base and adapted to engage said operatingmember, said base being further provided with a recess surrounding saidoperating member on the exterior of the base and a sealing washerdisposed in said last mentioned recess whereby said washer is shieldedfrom dirt or foreign matter to which the switch is exposed.

6. A thermostatic electric switch comprising a base, a bi-metalliccupped thermostatic disc member, grooved projecting members forsupporting said disc member in spaced relation to said base, a contactmember and operating means a sealing gasket surrounding said operatingmeans and resilient means'for effecting engagement between said sealingsurface and said gasket.

8. A thermostatic electric switch comprising a base having a chambertherein, cooperating contacts disposed in said chamber, an externallyextending operating member for said contacts, a bimetallic thermostaticdisc member operatively related to said operating member, a seal forsaid chamber associated with said operating member and resilient meansfor maintaining said seal until the operation of said contacts.

9. An electric switch comprising a base having a sealed recess, movablecontact members in said recess, a movable frictionless contact-operatingmember projecting through a wall of said recess, an annular sealingmeans carried by said contactoperating member and a seat in the recesswall against which the annular sealing means rests to provide a seal.

FRANCIS C. EVANS.

